The invention is based on a priority application EP06290101.2 which is hereby incorporated by reference.
The invention concerns a method for minimising the interference in a communications system according to the preamble of claim 1, a base station according to the preamble of claim 8 and a mobile station according to the preamble of claim 9.
OFDM air interfaces (OFDM=Orthogonal Frequency Division Multiplexing) are becoming increasingly important e.g. for the future development of air interfaces in 3GPP radio access networks (3GPP=Third Generation Partnership Project), for wireless local networks such as Wireless Local Area Networks (WLANs) according to standard IEEE 802.11a or for air interfaces of the fourth generation.
The capacity of a cellular OFDM system can be increased by the use of frequency selective algorithms for resource division, such as e.g. adaptive modulation, sub-carrier distribution or power control. In order to increase the capacity in areas in which high interference is expected, to reduce interference the interference coordination principle can be applied. This means that certain sub-carriers which belong to the same frequency pattern are used only with reduced transmission power in a cell. This reduction in transmission power admittedly leads to a deterioration in capacity in the region of the cell but in adjacent cells the interference for these particular sub-carriers is reduced, which increases the capacity there. The extent of the deterioration depends on the condition of the radio channels of the interfering base stations and on the frequency pattern that is used with the reduced power. This interference coordination principle requires coordination between the base stations involved. Other concepts for interference reduction are based e.g. on the principle of frequency hopping or special coding methods such as e.g. the so-called Costas sequences.
Conventional methods for interference reduction for OFDM interfaces are accompanied by a reduction in capacity above all in the peripheral regions of the cell. Costas sequences are furthermore only able to minimise the influence of interference, but do not allow adaptation or optimisation of the momentary use of the frequency resources.